Changes in extratemporal integrity and cognition in temporal lobe epilepsy: A diffusion tensor imaging study

Background: Diffusion tensor imaging (DTI) is a sensitive technique for studying cerebral white matter. Only a few studies have examined the association between changes in extratemporal integrity and cognition in temporal lobe epilepsy (TLE), especially in Chinese patients.
Aim: We used DTI to characterize microstructural changes and investigate their associations with cognition in patients with temporal lobe epilepsy.
Patients and Methods: We studied 27 adult patients with TLE and 21 healthy controls. A standardized neuropsychological evaluation and diffusion tensor imaging examination were conducted on each subject. Eight patients were excluded because T2-weighted magnetic resonance imaging (MRI) results showed visible lesions. Furthermore, we determined mean diffusivity (MD) and fractional anisotropy (FA) values in the different regions of interest - normal-appearing white matter (NAWM) in the frontal lobe white matter, the occipital lobe white matter, the corpus callosum, the internal capsules, the external capsules; and normal-appearing gray matter (NAGM) in the caudate nucleus head, the putamens and the thalami. These diffusion measurements were compared between the two groups, and we examined the correlations between DTI values and clinical characteristics. In addition, multiple linear regression analysis was used to study the association of DTI values with cognitive function.
Results: Compared with normal controls, TLE patients demonstrated decreased FA in NAGM of both thalami and NAWM of the posterior limb of the left internal capsule (P<.01). In patients with temporal lobe epilepsy, right thalamus FA showed a tendency to correlate with age at seizure onset (ß=0.47, P=.045), and left thalamus MD showed a tendency to correlate with the duration of epilepsy (ß=0.54 P=.038). Patients with temporal lobe epilepsy showed significantly poorer performance on nearly all tasks concerning category fluency and other executive functions (P<.01). In patients with TLE, there was a positive correlation between category fluency scores and FA in the white matter of the left frontal lobe (ß=0.429, P=.041) and the right occipital lobe (ß=0.613, P=.001).
Conclusions: Our results suggested that the thalamus might be a potentially important extratemporal structure involved in temporal lobe epilepsy. Moreover, a longer duration of epilepsy or an earlier age at onset may result in more abnormalities in the thalamus. Patients with temporal lobe epilepsy showed significantly poorer performance on nearly all tasks concerning category fluency and other executive functions. Our results showed that frontal lobe white matter contributed to category fluency impairment in patients with TLE, but other areas might also contribute to these impairments.

Keywords
Diffusion tensor imaging, executive function, temporal lobe epilepsy, thalamus